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<html lang="en">
<head>
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- <link rel="stylesheet" href="./outer.css"> -->
    <style>
        @import url(./outer.css);
        div{
            background-color: red;        
        }
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<body>
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     <div style="width: 100px;height: 100px;">块级元素</div>
    <div>块级元素</div>
</body>
</html>